The invention relates to a film composite for packaging purposes, effectively blocking the passage of water vapor and gases after sterilization in a water bath or in water vapor at temperatures of more than 90xc2x0 C., where the film composite has a barrier layer produced by vapor-deposition of inorganic materials. The scope of the invention also covers a process for producing the film composite, and its use.
In a known process for extending the shelf life of perishable products, for example food and drink, a sterilization process is carried out on the packaged product. For this, the contents, within their sealed packaging, are heated for a short time in an autoclave in hot water or water vapor at temperatures of up to about 130xc2x0 C.
The water vapor barrier, oxygen barrier or flavor barrier of the transparent film composite currently known and used for the packaging of food or drink is frequently insufficient after sterilizing treatment. An example of this is given by polymers of ethylvinyl alcohol (EVOH) and copolymers of EVOH and polyethylene (PE), which show impairment of barrier properties, in particular at high moisture level, and have a milky appearance. Coating gives better barrier properties in a film made from polyethylene terephthalate (PET) and coated with silicon monoxide, but these films show besides a yellowish discoloration in particular after sterilization at elevated temperatures a reduction in the level of barrier properties.
The object on which the invention is based is therefore to provide a film composite of the type mentioned at the outset which, compared with transparent film laminates of the prior art, has improved barrier properties in relation to water vapor, oxygen and flavors after sterilizing treatment.
The invention achieves this object by way of a film composite characterized in that the film composite encompasses a film made from polyethylene terephthalate (PET) with a coextruded layer made from polyethylene 2,6-naphthalate (PEN) on at least one side, and has a ceramic layer of from 10 to 200 nm thickness on at least one of the sides coated with PEN, said layer being produced in a vacuum from Al2O3 or from SiOx, x being a number between 0.9 and 2.